Heavy duty telescoping hydraulic hoists, such as are commonly used in dump trucks and the like, are typically composed of steel. Steel is a strong, relatively rigid metal which, when formed to a suitable wall thickness, provides the necessary support for the hoist and its load, and operates effectively under the extremely high hydraulic pressures to which such devices are subjected.
However, steel is also very heavy, which reduces the efficiency of vehicles such as dump trucks that have to carry the hoist when transporting a load. Moreover, steel corrodes at a fairly high rate, which reduces the life of the rings and seals that are used to contain the hydraulic fluid and to ensure that the stages move freely relative to one another, and reduces the durability of the hoist components in general.
It would accordingly be advantageous to construct a telescoping hydraulic hoist from a non-corrosive material which is lighter than steel. This would considerably reduce the weight of the hoist and significantly extend the useful life of many of its components. However, pure aluminum is too soft and weak to support the type of load that such hoists are designed to lift.
Aluminum alloys, which include an alloy composed of at least 75% aluminum and containing one or more other metallic elements such as copper, manganese, magnesium, silicon, zinc, and/or lithium, can be considerably stronger than pure aluminum. The additional metallic elements are known to substantially improve many mechanical characteristics of the alloy over pure aluminum, including its strength, particularly in the case of heat treatable aluminum alloys which can be processed to have a strength comparable to that of steel. However, the modulus of elasticity of aluminum is typically around one-third of the modulus of elasticity of steel. It is commonly believed that even heat treated aluminum alloys would deform under stresses which would not affect steel, causing the hoist to buckle under peak stresses which can be encountered during normal operation, and especially if the hoist malfunctions or if it is operated in an abusive or careless fashion.
In the heavy duty hydraulic hoist industry buckling is a major concern, and the low modulus of elasticity of aluminum alloys has resulted in the universal perception that such alloys are unsuitable for use in heavy-duty hydraulic cylinders. This perception includes low buckling point, and an inability to withstand the severe shocks, stresses and spikes in pressure that such hydraulic cylinders are subject to especially when used for dump trucks and other similar high stress applications. It is accordingly conventionally believed that such materials are unsuitable for use in heavy duty hydraulic hoist applications. As a result there are no heavy-duty aluminum hydraulic cylinders available in the market, although aluminum is in common use for light duty applications.
On the other hand, it is also common knowledge that in certain industries (such as the trucking industry), any significant reduction weight is extremely valuable because it increases available payload, and reduces fuel consumption and wear and tear on the vehicle. If it is proven to be feasible to construct heavy duty hydraulic hoists from high strength aluminum alloys, the weight saving over comparable steel hoists that are currently the standard would be substantial, potentially running into hundreds of tons. In addition, because aluminum does not rust, such a cylinder offers a significant environmental benefit since it would be feasible to employ a water based hydraulic medium that is environmentally friendly and less expensive than oil.